In the case where an image is projected onto a screen by a projector, when a person (e.g., a presenter who makes a presentation) is located between the projector and the screen, various problems are caused. To the presenter, for example, the glare of light projected from the projector is obstructive in making the presentation. In order to cope with such a problem, a technique of reducing the glare is known (e.g., PTL 1).